Periodic or random vibrations or shocks can excite the resonant frequencies in a rotatable storage article (such as the disk(s) in a disk drive), which can be problematic due to the resultant formation of undesirable stresses, displacements, fatigue, and even sound radiation. Such undesirable vibrations or shocks are typically induced by external forces and can be experienced by a wide variety of articles and under a variety of conditions. For example, resonant vibrations can cause excessive vertical displacement of an optical disk's surface during operation, which may lead to poor laser focus. Proper laser focus is a key to optimum write/read characteristics, signal quality, and tracking ability.
Various techniques have been used to reduce vibrational and shock effects (stresses, displacements, etc.) on rotatable storage articles. Three basic techniques to reduce vibration and shock effects include:
1) adding stiffness or mass to the rotatable storage article so that the resonant frequencies of the rotatable storage article are not excited by a given excitation source, PA1 2) isolating the rotatable storage article from the excitation source so the vibrational or shock energy does not excite the rotatable storage article's resonant frequencies, and PA1 3) damping the rotatable storage article so that given excitations from the excitation source do not result in excessive negative effects at the resonant frequencies of the rotatable storage article.
An isolation technique for limiting vibration transmission is described in U.S. Pat. No. 4,870,429. A single-sided or double-sided optical disk structure is described that includes two sheets of substrate bonded to each other with a foam spacer interposed between the two substrates to restrict or isolate the vibrations caused by external forces. The spacer is made from an elastomeric foam material and is positioned between the two substrates to restrict the transmission of such forces (e.g., vibrations or shocks). The thickness of the spacer is stated to be preferably not less than 0.2 mm, more preferably not less than 0.4 mm, because, when the thickness is too small, the effect of the spacer to restrict or isolate forces is not exhibited sufficiently. Such a system adds to the overall size of the rotatable storage article and may be impractical where close positioning of the article to other structures is desired.
Two types of surface or external damping treatments that can be used to reduce shock or vibration impact on rotatable storage articles are: (1) free layer damping treatments; and (2) constrained layer damping treatments. Both of these damping treatments can provide high levels of damping to a structure, i.e., dissipation of undesirable vibrations, without sacrificing the stiffness of the structure. The use of viscoelastic materials as exterior surface damping treatments is described in EP 0507515. Examples of additional surface or external damping techniques are described, for example, in U.S. Pat. Nos. 2,819,032; 3,071,217; 3,078,969; 3,159,249; and 3,160,549. However, all of the aforementioned damping techniques can add complexity and expense to the design of the rotatable storage article, limit the amount of exterior article surface available for data storage, and can increase the overall size of the article.
U.S. Pat. No. 5,725,931 discloses a constrained layer damper having slits and/or cutouts therein, which constrained layer damper provides improved damping performance. The constrained layer damper is useful for damping rotatable storage media, such as compact disks.
U.S. Pat. No. 5,691,037 and WO 96/21,560 disclose vibration damped laminate articles having improved force (torque and/or pressure and/or stress) retention, a method of making one article type, and novel tools used to make the one article type. The first laminate comprises at least one layer of damping material between at least two substrate layers. At least one deformation area is present in the laminate where the substrates are plastically deformed such that they are closer together than in non-deformed areas of the substrate and the damping material has less mass than in a non-deformed area of the article. The deformation area provides areas of good force retention for an attachment device attached thereto. The second laminate, which is not deformed, contains an additive of sufficient modulus, diameter and loading in its vibration damping layer to provide improved force retention. Spacer articles for disk drives are not discussed.
U.S. Pat. No. 5,538,774 provides a method for internally damping a rotatable storage article that is subject to resonant vibrations. The rotatable storage article, although capable of providing good damping, requires a redesign of the rotatable storage article to include the internal damping material, which can be costly to manufacture.
The typical method of providing spacing between disks in a disk drive type application involves the use of solid spacers between the disks. These spacers can be made from many materials, including aluminum, ceramics, stainless steel, rigid plastics, etc. These spacers, however, provide minimal vibration damping.
As the read and write tracks per inch (TPI) and the recording density of disks increase, there is a need to improve the vibration damping of disks economically and simply to implement the disks in existing and future disk drives. With new recording head technology, higher TPIs are possible (10,000-100,000 TPI and above). This now makes vibrations in disks more important to reduce, as vibrations in disks can reduce the TPI that can be reliably read and written. In the past, the spacers have been used to space the disks apart and provide some isolation or improved thermal expansion properties to prevent disks, such as ceramic disks, from breaking.
For example, U.S. Pat. No. 5,663,851 discloses a disk drive spindle hub assembly for a hard disk drive that includes a spindle hub with a stack of information storage disks journaled about the spindle hub in a spaced-apart, vertically aligned relation. Annular spacers are positioned between adjacent information storage disks in order to space the disks apart in the vertically aligned relation of the spindle hub. A disk clamp is configured to concentrically clamp the stack of information storage disks in axial alignment with the spindle hub. A dummy disk comprising an arrangement of a metal plate, a damping portion, and a polyester film is disposed between the disk clamp and the storage disk in order to absorb spurious vibrations and minimize stress concentrations and disk distortion when the storage disks are mounted for rotation within the hard disk drive.
Newer drive rotation speeds of 7,200 and above revolutions per minute (RPMs) plus increased shock requirements (500 to 1,000 or more g of force) require a high force retention in the spindle assembly to prevent disks from slipping or shifting on the spindle. Shipping or shifting can cause data location to be lost or degraded, hindering read/write performance and/or drive reliability.
U.S. Pat. No. 5,367,418 discloses a hub assembly that incorporates o-rings that can absorb external loads applied in either an axial or radial direction relative to the hub.
U.S. Pat. No. 5,590,004 discloses a resilient clamping member positioned between a spindle flange and the upper side of a disk, with a compliant element supported by the spindle rim and contacting the lower side of the disk.
U.S. Pat. No. 4,945,432 discloses a spacer design that serves as a buffer when the magnetic disks and the spacers are compressed together. The substrates of the magnetic disks are made of non-metallic materials, such as glass or ceramics, but do not break easily by the motion of the spindle or the change in temperature because either the 1) adhesive used to form a unistructural assembly of the magnetic disks or 2) spacers or elastic members inserted in annular indentations formed in the spacers serve as buffers when the magnetic disks and the spacers are compressed together.
U.S. Pat. No. 5,422,768 discloses a compliant hard disk assembly for a recording/reproducing device. According to the abstract, to minimize unwanted motion in a hard disk assembly in a hard disk drive, an elastomeric support is employed to mount a hard disk pack for rotation by a motor rotor of a disk spindle motor. The hard disk pack includes a hard disk support ring that has opposite annular axial faces upon which the hard disks are securely mounted and axially spaced thereby. An elastomeric connection between the hard disk support ring and a cylindrical body of the motor rotor of the disk spindle motor provides a soft, or compliant, support for the hard disk pack.
A need exists for a spacer articles that address the needs of newer hard disk drives that have higher TPIs (greater than 10,000 TPI, typically 17,000 or more TPI) and higher RPMs (greater than 5,000 RPM, typically 7,200 RPM or higher) that lead to more disk vibrations as drive disk capacity increases. There is also a need for thinner disks to allow more disks in a drive format height. The disks need to be adequately damped to provide a minimally vibrating surface for reading and writing information or the drive will not be able to perform at the next level of capacity that is now needed to meet growing industry demands for a low cost megabyte of memory.